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Engineered nanomaterials (ENM) represent a significant breakthrough in
material design and development. The quantum properties that emerge from their
scale, precise architecture, and engineering attributes provide considerable
opportunity to solve problems in such diverse areas as medicine, electronics,
energy, space exploration, water purification, and food storage. Numerous
research articles have examined the sensitivity of the relationship of scale,
structure, composition, and emergent properties of nanomaterials to their
behavior in biological systems and the environment.
This relationship between precise design and behavior has led to the proposal
that nanomaterials can be engineered to be Safe By Design (SxD), that is,
designed to maximize their benefit in problem solving and product development
while posing minimal risk to human health and the environment. While SxD is an
extremely attractive concept, it may be useful to examine the assumptions that
underlie it, as well as the consequences that might be engendered by it. The
proceeding examination is necessarily selective and intended to be thought
provoking, not comprehensive.
Firstly, SxD presupposes the existence of crosscutting design principles for
ENM in biological systems. It suggests that, in contrast to the concept of a
sensitive design-behavior relationship, that there are physical and chemical
properties of ENM, or a subset of such properties, that support a given
biological behavior in multiple microenvironments. Given the exponential number
of combinations of physical and chemical properties possible for an ENM, this
assumption seems plausible, albeit challenging to test on a scale that would be
definitive.
SxD also suggests that researchers can identify the physical and chemical
properties, or the subset of properties, that produce distinct sets of
beneficial or adverse effects. Biologically, one might anticipate that the ENM
properties designated beneficial or adverse represent two ends of a continuum,
with most of the biological behavior occurring between the two poles. (For
example, consider a continuum from positive to negative surface charge or from
hydrophillicity to hydrophobicity.)
Additionally, SxD assumes that the adverse effect can be engineered out
through manipulation of physical and chemical properties while the beneficial
properties are maintained. This line of thought suggests that modifications to
an ENM that "tweak" a product to decrease risk of an adverse effect can be made
without significantly changing the benefit the ENM confers on a product.
If this proves true, it would seem to imply that there are limited unique
design solutions but multiple combinations of physical and chemical properties
that produce the same effect. The SxD challenge then would be to identify the
sets of physical and chemical properties that produce the same outcome in
multiple microenvironments, as well as the combination of physical and chemical
properties that produces multiple, microenvironment-dependent outcomes.
As a final consideration, increasing attention is being given to life cycle
analysis of an ENM, or to potential changes in physical and chemical properties
as ENM move through the environment or the human body. Recent research suggests
that when an ENM is exposed to a microenvironment, a corona of inorganic
environmental substances or biological molecules form around the ENM; that the
composition of this corona is a function of the ENM surface properties and the
microenvironment; and that the biological response to the ENM is a function of
molecules comprising the corona. This hypothesis provides support for SxD in
that the number of molecules that could form the corona is more limited than the
possible combinations of physical and chemical properties, as well as
modifications and derivatives of ENM that could be constructed.
SxD is an intriguing concept with the potential to guide ENM product design
and development to maximize benefit and minimize risk to humans and their
environment. Broad principles that relate physical and chemical properties to
behavior could be determined from careful selection and testing of ENM and
microenvironments, however one should consider the cost benefit ratio that would
underlie this extensive investigation of design principles in contrast to the
perhaps less expensive product-specific analysis of risk and benefit.
Copyright AZoNano.com, Dr. Sally Tinkle (National Institute of
Environmental Health Science, National Institutes of Health)